1. Field of the Invention
The present invention generally relates to battery protection devices, battery protection systems using the battery protection devices, and battery protection methods, and more particularly, to a battery protection device, a battery protection system, and a battery protection method that detect overcharge and over-discharge of a battery and control a switching element.
2. Description of the Related Art
In terms of its energy density and charging/discharging characteristics, lithium ion batteries have been attracting attention as secondary batteries that are repeatedly used by being charged. However, since the characteristics of lithium ion batteries are apt to be degraded due to over-discharging and overcharging, it has been necessary to protect lithium ion batteries with battery protection systems.
FIG. 1 is a circuit diagram of a conventional battery protection system 1.
In the case where n batteries 11 are connected in series in the conventional battery protection system 1, both ends of each of the n batteries 11 are connected to corresponding terminals T11 through Tn+1, thereby monitoring the n batteries 11 with a protection IC 12. When the protection IC 12 detects an over-discharged state or overcharged state of the n batteries 11, terminals T21 and T22 supply abnormality detection signals to driver circuits 13 and 14, respectively. The driver circuits 13 and 14 control the gate voltages of MOS transistors M1 and M2 in accordance with the abnormality detection signals from the terminals T21 and T22 of the protection IC 12, thereby turning OFF the MOS transistors M1 and M2, respectively. The drains and sources of the MOS transistors M1 and M2 are connected in series between the batteries 11 and a terminal T1. When the MOS transistors M1 and M2 are turned OFF, the batteries 1 and the terminal T1 are disconnected, and discharging or charging is stopped. In the aforementioned manner, the batteries 11 are protected from discharging and overcharging.
In the battery protection system 1 as shown in FIG. 1, it is necessary for the single protection IC 12 to protect the batteries connected in series. Thus, when the number of batteries is increased, a high voltage is applied to the protection IC 12, and the protection IC 12 may not be able to withstand the high voltage. Hence, it has been possible to protect merely several batteries connected in series. Accordingly, there is a demand for a battery protection system capable of protecting a large number of batteries connected in series.
As for battery protection systems capable of protecting a large number of batteries connected in series, there has been proposed a system for protecting batteries by performing abnormality detection by: dividing portions to be detected into blocks for each battery; sequentially transmitting abnormality detection information from a high-voltage side to a low-voltage side; and turning OFF a switching element connected in series to the batteries in response to the abnormality detection information output from the last block (refer to, for example, Japanese Laid-Open Patent Application No. 2001-307782).
However, since conventional battery management systems perform level shifting by detecting the voltages of the adjacent protection blocks, there have been problems in that it is difficult or impossible to separately drive blocks and that wiring becomes complex.
Additionally, it has been necessary in conventional battery management systems to connect plural protection blocks in a predetermined order.